In many cases, a craftsman is required to fit a series of screws in a workpiece, but must predrill tap holes in the workpiece to enable rapid and true driving of the screws. This necessity occurs frequently in woodworking, for example in fixing molding around a door, or placing decorative facie on furniture, or hanging a door. Sheet metal workers also must predrill screw holes essentially every time a piece of sheet metal is affixed to backing with screws, for example when placing a metal roof. Tap holes are also drilled in plastic, plaster, and other materials of construction prior to setting of screws. In some cases, when it is important to have the head of the screw flush with or slightly below the surface of the workpiece, a countersink may be used either instead of, or in addition to, the tap hole drill.
As a craftsman moves along a workpiece, it is necessary for him to first drill (or countersink) a tap hole, and then drive the screw; then he moves to an adjacent location and repeats the drill/screw sequence. He must either repeatedly change the bit in the power tool from drill bit to screwdriver bit or he must have two, or, if a countersink is to be used in addition to the drill, three power tools each equipped with a different bit. In many cases, it will not be convenient to have multiple power tools, and the constant changing of the bits is unduly time consuming.
Accordingly, it is an object of the invention to provide a quick connect-disconnect coupling device for connecting a rotary cutting bit, such as a drill or countersink bit, to the bit of a power screwdriver.